In the ongoing miniaturization process of integrated circuit devices, the latest developments involve the manufacture of multiple stacks of ultrathin silicon dies having thicknesses reduced to sub 100 micron, or even in the 10-50 micron zone. This stacking of ICs in a package is also referenced as 3D stacking. For a 3D stack to be functional, vertical connectors, known as Through Silicon Vias (TSVs) are necessary, as well as additional layers of horizontal interconnecting structures. Generally, a TSV can be seen as a through hole through the thin die; this hole structure typically needs a wall liner treatment, in the remainder also referenced as cladding which may include for example, a barrier layer, isolation layer or seed layer. In addition, the TSV is provided with a filling of a conductive matter such as Cu. The width of a TSV is typically sub 10 micron, and a filling resolution of 2-5 micron is therefore desired.
To obtain such resolution WO2011/145930 proposes a chip die TSV treatment apparatus arranged for treatment of TSVs in chip dies in a chip manufacturing process.
The apparatus comprises a carrier plate arranged for placement of a wafer having identified TSVs to be treated. The apparatus further comprises a donor guiding system for guiding a donor over a TSV to be treated. The guiding system is adapted to keep the donor distanced from the wafer top surface. The apparatus further comprises an alignable laser system arranged for impinging a laser beam on a side of the donor opposite a side facing the wafer. The laser beam is tuned in timing, energy and direction to generate donor matter directed towards the TSV. A control system is provided for aligning the laser beam and the donor guiding system relative to the TSV. In an embodiment, the alignable laser system in the known apparatus comprises a fast beam modulator, such as a galvano mirror, polygon mirror, acousto-optic or electro-optic modulator that provides a scanning movement of the laser beam in a first direction. In practice each single TSV is treated by a multishot process where repeated steps are provided of guiding fresh donor material relative to the TSV.
FIG. 1 schematically shows a chip die TSV treatment as disclosed in the cited document. The known treatment comprises clamping a wafer 110 having identified TSVs 100 to be treated. The TSVs are typically provided in a basic pattern that is repeated, wherein each basic pattern corresponds to the TSVs for a single die of a plurality of dies to be manufactured from the wafer. The treatment subsequently comprises providing a donor 130 distanced from the wafer top surface 111; aligning the laser beam 102 of the laser system 120 and guiding the donor 130 relative to an identified TSV 100 on the wafer 110; and impinging a laser beam 102 on a side 131 of the donor 130 opposite a side facing 132 the wafer 110; the laser beam 102 tuned in timing, energy and direction to generate donor matter in the form of a plasma 140 directed towards a TSV 100 to be treated, in order to provide the TSV with a cladding. Accordingly, a plasma 140 is generated of a donor 130 preferably chosen of a group of Tantalum (Ta), Tantalum Nitride (TaN), Titanium (Ti), Titanium Nitride (TiN). The clamp 112 may be made of silicon, glass or epoxy based support. In an embodiment, the clamp 112 is a vacuum clamp, for example, of porous aluminum, where a vacuum is provided underneath the wafer 110 and transferred to the clamping zones 114 via channels 113.
FIG. 1A shows the treatment in more detail, here as a process subsequent to the cladding treatment of FIG. 1. Therein the TSV 100 is filled with a conductive material 200 such as Copper wherein subsequent donor matter 231 is directed towards a TSV 100 by directing particles 231 of a subsequent donor 230 into the TSV 100. Preferably, the cladding and filling step are performed in the same process environment 300 with subsequent donors 130, 230. Accordingly, in this process, the TSV treatment involves filling the TSV 100, by having donor matter 231 directed towards a TSV 100 to be treated. In a multishot process repeated steps are provided of guiding fresh donor material 230 relative to the TSV 100 and impinging the laser beam 102 on the donor 230 so as to direct a particle 231 of donor matter into the TSV 100. Suitable conductors 200 include Copper, Aluminum, Tungsten, Chromium, Polysilicon. To carry out the method in a suitable way for via filling purposes and for vias having a typical diameter in the range of 5-15 microns, an aspect ratio of 1:5-1:10, and a depth typically in the range of 20-100 microns, filling droplets preferably range between 2-10 micron. To achieve cost-effective filling at a rate of at least 1000-3000 vias per second, a laser repetition rate is preferably at least 60-600 kHz. For filling TSVs droplets may be used having a typical diameter of 2-10 micrometer.
FIG. 2 schematically shows a method as disclosed by the above-cited document. As schematically illustrated therein, a laser beam 102 is directed towards a scanning stage having a wafer 110 clamped thereon. A fast beam modulator 400 (galvano mirror, polygon mirror, acousto-optic or electro-optic modulator etc.) provides a scanning movement of the laser beam 102 in a first direction (x). Each single TSV 100 is treated by a multishot process where repeated steps are provided of guiding fresh donor material 230 relative to the TSV 100 and generating a particle 231.
In Step (1) as show in the top left figure, the donor 230 is kept fixed relative to the wafer surface 111, and the laser beam 102 is scanned over the various TSVs 100 by a tilting movement of a beam modulator 400.
As shown in the top right figure the donor 230 is shifted relative to the wafer 110 in the direction x.
In Step (2), as shown in the middle left figure, the scanning steps are repeated after the donor 230 is shifted relative to the wafer 110. Thus fresh donor material 230 is directed to each TSV 100.
As shown in the middle right figure the donor 230 is shifted a further step relative to the wafer 110 in the direction x.
In Step (3) the same scanning movement is repeated with the donor material 230 shifted a further step.
Accordingly, after each scan of the laser beam, wherein a series of TSV is partially filled, the donor guiding system shifts fresh donor material in front of the TSVs to be filled. The cited document notes that the shifting steps can be performed in both planar directions to cover the entire wafer surface. Alternatively, the wafer can be continuously moved in a direction perpendicular to the scanning beam movement. In practice a relatively high number of shots is necessary to fill each TSV (e.g. in the number of 100). As a result, the donor 230 has to be transported at a high speed, e.g. 10 m/s or more along the wafer to be treated in order to supply fresh donor material at a sufficient rate to achieve a sufficient productivity. A strip thereof having a width corresponding to the spot size of the laser beam, e.g. in the order of 10-20 micrometers is used for providing the donor material. This requires large stocks with donor material. An efficient use of donor material is desirable. However, re-use by re-routing processed donor material requires a very rapid and precisely controlled feedback system to ensure that donor material to be ejected is always present.